Optical data-reading systems have become an important and ubiquitous tool in tracking many different types of items, and machine-vision systems have similarly become an important tool for tasks such as part identification and inspection. Both optical data-reading systems and machine vision systems capture a two-dimensional digital image of the optical symbol (in the case of an optical data-reading system) or the part (in the case of a general machine-vision system) and then proceed to analyze that image to extract the information contained in the image. One difficulty that has emerged in machine vision systems is that of ensuring that the camera acquires an accurate image of the object; if the camera cannot capture an accurate image of the object, the data-reading or machine-vision system can be unable to decode or analyze the image, or can have difficulty doing so.
One of the difficulties in acquiring an accurate image is ensuring that the object being imaged is properly illuminated. Problems can arise when a system is used to image a variety of different symbols, because for a given system the lighting may or may not be of the right type. A system with bright field illumination will find it difficult or impossible to image an object that requires dark-field illumination, while a system with dark field illumination will find it difficult or impossible to image an object that requires bright field illumination. Illuminators used with existing optical data-reading systems and machine vision systems tend to be capable of bright field illumination or dark field illumination, but not both. Users must therefore keep two separate systems on hand so that they will have one with the correct kind of lighting.